Backlash-eliminating mechanism for machine tools



June 27, 1939. F. s. HAAS 2,163,836

I -BACKLASH-ELIMINATING MECHANISM FOR MACHINE TOOLS Filed June 25, 1957 INVENTOR. FREDERICK S. HAAs ATTORNEY.

Patented June 21; 1939 UNITED STATES,

PATENT OFFICE 1 amass: BAOKIASlI-EIJIIINATING MECHANISM FOR momma 'roons k Frederick Salinas, Cincinnati, Ohio, assignor to Cincinnati Grinders Incorporated, Gin Ohio, a corporation of Ohio I Application June 2:, 1631, semi no. 149,848 9 Claims. (cl; 9o:2)

This invention relates to on mechanism and more particularly to the elimination oi. backlash from such mechanisms as are utilized for the propulsion of precision machine tools.

One of the objects of this invention is to provide backlash eliminating mechanism which is simple and compact in construction; easy to adjust; has long life; and is adjustable for wear.

Other objects and advantages of the present 10; invention should be readily apparent by reference to the iollowing specification considered in conjunction with the accompanyin drawing illustrative of one embodiment thereot but it will be understood that'any modifications may be made in the specific structural details within.

the scope of the appended claims without departing from or exceeding the spirit of the invention.

Referring to the, in which like reference numerals indicate like or similar parts: x

Figure lis a sectionalviewthrough amachine tool showing an embodiment of the invention.

Figure 2 is a detail section on the line 2-2 or FigureL- a 3 Flgure3isadetailsection online'3-4 01' Fig- Figure 4 is a plan view showing portions of the diilerent control elements in section in order to illustrate the method of adjustmenh lnl 'igureloi'thedrawingthercisshownin section a portion offs conventional *machine structure indicated by the reference numeral ll, saidstructurehavingguideways II and I2 formed mtheieonlorsupportingamovetleelide is. This slide may be in the formof a conventional tabl Y of a precision grinding-machine.-

Any suitable form of power mechanismmayheutilizedioractuatingthe table, and such on is'illustrated in the a's terminating"!!! the drive shaft ll.

Q 'lh'etabie ll hasa rackbar is attached tothe under side thereof and this invention contema simpleand compact in for coupling thedrlve shaft to the rack bar'witllouti lostmotion. To this end a sleeve It is supported byantifrictionbearingslland llintllemachine structure llandinlightaugularrelationtothe' 'lheupperend of'thesleevehasapinionllsecuredthereto;

I direction of movement of thetable.

Thepinimimaybeaseiiaratekeyedto 5o theendofthesleevemritmaybeintigraltherewlth,asshowninthe drawing. .Thepinionll intermesheswiththeteethmtherackbarll. The lower end oifthesleeve carries atoothed memberinthei'orm otawormgea'rllwhich s inwithawormlliimedwiththedrive being twisted relative .to the other end.

which, as shown inFlgure 2, has a worm 23-mtatably mounted therein and intermeshing with the teeth 24 of a worm wheel 25 which is formed integral with the sleeve l6. The-worm 23 has an enlarged head 26 which forms a'shoulder abutting the side of the hub 22, and a reduced end 21 which passes through a bore 28 formed in the hub, and is threaded to receive a nut 29. To iacilitate assembly of the parts and insure a neat ilt of,the worm wheel 2| onthe sleeve, the hub has a keri 30 cut therein which divides the lower 'portion'oi the hub into two parts 3| and 32, the same being adapted to be drawn together by'a bolt 33 which is threaded into one of the parts. 15.

' spaces 39 exist between the-side of thepin and the lower portionof the'sleeve IG. The pin may -.be held in position by a set screw ll threaded into the lower end oi the member.

Thebacklash is eliminated from the driving .mechanism by rotating theworm 23 in such a direction that the re-active.thrust will cause counterclockwise rotation of the hub 22 and clockwise rotation of the sleeve it. Such a reactive thrust will cause the teeth ll oi worm wheel a. to tightlyengage the lower side ll of the thread of worm 2|. Since movement inthis direction cannottske place, the worm II will act asanabutmenttocauserotationoithesleeve II Clockwise rotation of the sleeve I wlllrault in clockwise rotation of the pinion I, as viewed in Fjigure 4, and thereby movement of the rack II in a direction indicated by the arrow 43.. Die torsion member 35 is connected with the worm gear Ilbymeans oipinILasshowninFlgure 3, and therefore during this, rotary adjustment of the sleeve relative to the worm gear, the pinion 34 secured to the upper end of the torsion member will remain stationary. This means that the pinion II and rack Ii will advance ina general clockwise direction relative to the pinion :4. It

will be obvious that durln'g'this advancing "adjustlnent that the forward side of the teeth of pinion'l! will be in engagement with the upper shaft u. The gear at has an elongated hub 22 "in'a clockwisedirectimasviewe'd'inl igure2 vsideof the rackteeth,asviewedinl igure 4. This 66 movement will continue until the under side of the rack teeth engage one side of the teeth on pinion 34. If the adjustment is carried far enough, it will thereby cause, rotation of pinion 34 in a clockwise direction. Since the lower end of the tension member is held against rotation? this will introduce a tension in the member and act to restrain further adjustment of pinion l9. The result, however," will be that the teeth of one pinion will be in tight engagement with one side of the, rack teeth and that the teeth of the other pinion will be in tight engagement with the other side of the rack teeth, whereby all lost motion is eliminated from this mechanism.

In order to simplify the explanation, it ,was assumed that the gear H was held against rotation by the worm 42, but it is to be understood that the backlash eliminating mechanism is a self-contained unit and does not necessarily depend upon the assistance of worm 42 when preloading the same. In other words, if the worm gear 42 were removed and the adjusting worm 23 rotated, it will be apparent that a relative movement between the sleeve 18 and the worm 20 will take place. and if the pinion l9 and rack i5 were held against movement by the friction of the slide, it will be apparent that the worm gear 20 would then be the movable member, and would move through space in a counterclockwise direction as viewed in Figure 4. This would cause rotation of the pin 38 integral with the gear and thereby a rotation of the tension member and pinion 34 in a counterclockwise direction until the pinion 34 engaged one side of the rack teeth.

Further rotation of the adjusting worm 23 would cause arelativ e separation between tooth 44 of pinion i9 and tooth 45 of pinion 34, or in other words, oppositedirections of rotations of the two pinions, resulting in elimination oi any'lost motion. The parts would be held in this position by the torsion member 35. The worm gear 20 and the pinions 22 may now be rotated as a unit as by the worm gear 42 to cause movement of the slide.

There has thus been provided an improved backlash eliminating mechanism which is easy to construct and operate, which is inexpensive,

' and which has long life.

1. In a machine tool having a translatable slide, a support therefor, and a rack bar attached to the under side of said slide, the combination of a sleeve antifrictionally supported in said support and having a pinion attached to one end in intermeshing relation with said rack and carrying a driver at the other end, a torsion member passing through said sleeve and carrying a second pinion intermeshing with said rack in coaxial relation to the first pinion, positive means inter- 6o connecting the other end of said torsion member to said driver and independently of said sleeve,

a worm and worm gear for eflfectingrelative adjustment between the driver and sleeve to thereby place a torque on said torsion member, whereby said pinions will be continuously urged in opposite rotative directions into engagement-with opposite sides of the teeth on said rack, whereby backlash will be eliminated "between said drive a and said rack, and a power operable member for rotating said driver. 2. The combination with a machine tool -in-' a cluding a' support and a member translatable thereon, of an anti-backlash transmission ior.

eifecting relative movement of said parts, ineluding a driving member, a pair of co-ax'ial aieasse driven members, and means intervening the driving and driven members for effecting an out-oiphase relative urge of said driven members including a positively driven power transmitter coupled with one of said members, a torsion rod having one end connected to the other of said driven members, and means for imparting a variable relative axial twisting movement to the other end of the rod and said transmitter, whereby the relative outmI-phase urge of said driven members may bevaried as desired.

3. The combination with a machine tool including 'a support and a member translatable thereon, of an anti-backlash transmission for efi'ecting relative movement of said parts including a driving member, a pair of co-axial driven members, and means intervening the driving and 'driven members for efiecting an out-ot-phase relative urge of said driven members including a positively driven power transmitter coupled with one of said members, a torsion rod having one end connected to the other of said driven memportion, a driven member carried by said tubular member, and a second driven member adjacent the first, a resilient rod coupled with said second. member and telescoping within the tubular member, means directly connecting the rod with the hub at a point remote, from the driven member, transmission means engaging said pair or driven members for limiting their potential relative movement, and means for eflecting' a relative movement between the sleeve and red at the hub whereby a variable torsion is set up in the rod creating a variable out-of-phase urge as respects the driven members on the rod and sleeve.

5. 4 In a backlash transmission for machine tools including a driven gear having an axially ofiset hub portion, substantially co-extensive telescoped members each having one terminus extending within said hub, driven members carried by the remote ter'minii of said telescoping members, a transmission member'interlocking with said pair of'members and limiting their potential relative movement, means for securing one of said telescoping members in fixed position with respect,

' members at'the hub, wherebya variable torsional strain may be created between said telescoping members to urge their driven members into outof-phase relationship with a selectively variable force.

- 6. In a backlash transmission for machine tools including a driven gear having an axially offset, hub portion, substantially co-extensive telescoped members each having one terminus extending within said hub, driven member's carried by the remote terminii of said telescoping members, a transmission member interlocking with said pair oi members and limiting their potential relative movement, mean{ for securing one of said telescoping members in fixed position with respect to the hub} an adjusting mechanism intervening ing variable relative rotation of the members at I the hub, whereby a variable torsional strain may be created between said telescoping members tov urge their driven members into out-oi-phase relationship with a selectively variable force, said hubhaving a slot formed therein permitting of expansion and, contraction thereof, and means for contracting the hub to clamp the telescoping members in preselected relatively adjusted position.-

7, An anti-backlash transmission for the purpose described including a driving member, a final driven member having a toothed element, a pair of pinions intermeshing. with said element, a resilient couple urging said pinions into out-ofphaserelationship, means remote from the pinions and final driven member for variably determining the force of resilient out-of-phase urge of said couple, and driving connections between i the driving member and said pinions for effecting joint uni-directional actuation thereof.

8. A mechanism of the character described, the combination of a pair of relatively shiftable pinions, of a member having a toothed portion joint- 1y engaged by said pinions for actuation thereby;

means tensionable to produce an out-oi-p'nase relative urge of the pinions, a first means for variably determining the tension effecting said out-ofphase urge, a second means for locking the means in preselected tensioned condition, and a common driver coupled with the pinions for eifecting joint uni-directional actuation thereof.

, 9. A backlash eliminating transmission of the character described, including a driven member having a toothed portion, a torsion rod'having a pinion thereon meshing with said toothed member, a sleeve circumscribing the rod carrying a second pinion in mesh with said toothed member, said member jointly engaging said pinions and limiting their potential relative rotational movement, a driving member, means for securing one of the pinion bearing elements to the driver, an adjusting mechanism for varying the rotary adjustment of the other pinion bearing element with respect to the driver whereby opposed torsional strains are set up in the rod and sleeve elements when the pinions are in mesh with the transmission member, and means for locking the second pinion bearing element and driver in any position of relative adjustment thereof.

FREDERICK S. I-IAAS. 

